Alkylation Process with Recontacting in Settler

ABSTRACT

A system and/or process for decreasing the level of at least one organic fluoride present in a hydrocarbon phase contained in an alkylation settler by contacting the hydrocarbon phase with an HF containing stream, containing greater than about 80 wt. % and less than about 94 wt. % HF, in the intermediate portion of the settler which contains at least one tray system, with each tray system comprising a perforated tray defining a plurality of perforations and a layer of packing below the perforated tray, are disclosed.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a Division of copending application Ser. No.11/047,514 filed Jan. 31, 2005, the contents of which are herebyincorporated by reference in its entirety.

BACKGROUND OF THE INVENTION

The present invention relates to a method and/or system for thealkylation of an olefin with an isoparaffin utilizing an acidic catalystmixture. In another aspect, this invention relates to a method ofreducing the concentration of organic fluorides in an alkylate product.

The use of catalytic alkylation processes to produce branchedhydrocarbons having properties that are suitable for use as gasolineblending components is well known in the art. Generally, the alkylationof olefins by saturated hydrocarbons, such as isoparaffins, isaccomplished by contacting the reactants with an acid catalyst to form areaction mixture, settling the reaction mixture to separate the catalystfrom the hydrocarbons, thereby forming a catalyst phase and ahydrocarbon phase. The hydrocarbon phase is further separated, forexample, by fractionation, to recover the separate product streams.Normally, the hydrocarbon phase of the alkylation process containshydrocarbons having five to ten carbon atoms per molecule. In order tohave the highest quality gasoline blending stock, it is preferred forthe alkylate hydrocarbons formed in the alkylation process to be highlybranched and contain seven to nine carbon atoms per molecule.

It has long been known that recontacting an alkylate stream containingorganic fluorides with hydrogen fluoride is an effective method toreduce the concentration of organic fluorides in such alkylate stream.In order to ensure adequate contact of the alkylate stream with thehydrogen fluoride, the industry has most typically chosen to use aneduction system in a separate recontacting vessel wherein hydrogenfluoride is educted into a flowing alkylate stream followed byseparation of the alkylate from the hydrogen fluoride by gravityseparation.

It is generally desirable to minimize the number of vessels containinghydrogen fluoride which are present in an alkylation unit. Therefore,development of an improved process and/or system for effectivelyrecontacting alkylate with hydrogen fluoride without using an additionalhydrogen fluoride containing vessel would be a significant contributionto the art.

BRIEF SUMMARY OF THE INVENTION

It is, thus, an object of the present invention to provide an improvedprocess and/or system for reducing the concentration of organicfluorides in an alkylation product.

A further object of this invention is to provide an improved processand/or system for reducing the concentration of organic fluorides in analkylation product wherein the alkylate is recontacted with hydrogenfluoride within a settler vessel allowing the HF used for recontactingto be de-inventoried with the acid catalyst in the settler vessel in theevent a rapid acid transfer is required.

In accordance with a first embodiment of the present invention, a systemis provided including the following: a) an alkylation reactor; b) asettler, having an upper portion, an intermediate portion, and a lowerportion wherein the intermediate portion contains at least one traysystem comprising a perforated tray defining a plurality of perforationsand a layer of packing below the perforated tray; c) a feed conduitoperably related in fluid flow communication to the alkylation reactor;d) a settler feed conduit operably related in fluid flow communicationto the alkylation reactor and to the intermediate portion of the settlerat a location below the lower-most tray system; e) an HF feed conduitoperably related in fluid flow communication to the intermediate portionof the settler at a location above the upper-most tray system; f) analkylate containing product conduit operably related in fluid flowcommunication to the upper portion of the settler; and g) an alkylationcatalyst conduit operably related in fluid flow communication to thelower portion of the settler and to the alkylation reactor.

In accordance with a second embodiment of the present invention, aprocess is provided including the following steps: a) contacting ahydrocarbon feedstock comprising an olefin and an isoparaffin with acatalyst comprising hydrogen fluoride in an alkylation reaction zone tothereby produce alkylation of at least a portion of the olefins andisoparaffins in the form of an alkylation reaction effluent; b)providing a settler, having an upper portion, an intermediate portion,and a lower portion wherein the intermediate portion contains at leastone tray system comprising a perforated tray defining a plurality ofperforations and a layer of packing below the perforated tray; c)passing the alkylation reaction effluent from the alkylation reactionzone to the intermediate portion of the settler at a location below thelower-most tray system and permitting a phase separation to occur so asto produce a catalyst phase and to produce a hydrocarbon phasecomprising alkylate and organic fluorides; d) passing an HF containingstream comprising greater than about 80 wt. % and less than about 94 wt.% hydrogen fluoride to the intermediate portion of the settler at alocation above the upper-most tray system; e) permitting at least aportion of the hydrocarbon phase to coalesce under each perforated traythereby providing a hydrocarbon layer under each perforated trayenabling a steady state volume of hydrogen fluoride to collect on thetop surface of each perforated tray; f) for each of the tray systems,permitting at least a portion of the hydrocarbon layer to pass upthrough the perforated tray in the form of droplets for contact with thesteady state volume of hydrogen fluoride; g) permitting a treatedhydrocarbon phase to pass up out of the intermediate portion of thesettler; and wherein the cumulative contact time of the hydrocarbonphase with hydrogen fluoride contained in the steady state volumes ofhydrogen fluoride in the intermediate portion of the settler is greaterthan or equal to about 0.5 seconds, and wherein the treated hydrocarbonphase contains less organic fluorides than the hydrocarbon phase; h)removing the treated hydrocarbon phase from the upper portion of thesettler; i) removing the catalyst phase from the lower portion of thesettler; and j) using a portion of the catalyst phase as at least aportion of the catalyst in the alkylation reaction zone.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a simplified schematic flow diagram presenting an embodimentof the present invention.

FIG. 2 is a section taken across line 2-2 of the simplified schematicflow diagram of FIG. 1.

FIGS. 3 (a)-(f) are perspective views each illustrating an alternativeconfiguration of packing elements useful as packing in the presentinvention.

DETAILED DESCRIPTION OF THE INVENTION

According to the first embodiment of the present invention, the systemof the present invention will be described with reference to the FIGS. 1and 2.

Referring to the FIG. 1, therein is illustrated the inventive system orapparatus 10 including an alkylation reactor 100 having an inside wall102 which defines an alkylation reaction zone. The alkylation reactor100 is operably related by connection in fluid flow communication to afeed conduit 104 for introducing a hydrocarbon feedstock into thealkylation reaction zone. The alkylation reactor 100 provides means foralkylating at least a portion of the hydrocarbon feedstock to therebyproduce alkylation of at least a portion of the olefins and isoparaffinsin the form of an alkylation reaction effluent.

The alkylation reactor 100 is operably related by connection in fluidflow communication via a settler feed conduit 106 to an intermediateportion 108 of a settler 110. Settler feed conduit 106 is for removingthe alkylation reaction effluent from alkylation reactor 100 and forintroducing the alkylation reaction effluent into intermediate portion108 of settler 110 at a location below the lower-most tray system 112contained in intermediate portion 108. Intermediate portion 108 containsat least one tray system 112 and each tray system 112 comprises,consists of, or consists essentially of a perforated tray 114 defining aplurality of perforations 116 (as shown generally in FIG. 2) and a layerof packing 118 below each of the perforated trays 114. Packing elementsuseful as packing 118 can be selected from the group consisting of pallrings, raschig rings, berl saddles, intalox saddles, tellrettes, andcombinations of any two or more thereof and are depicted in FIGS. 3(a)-(f). Packing 118 can also comprise structured packing definingmultiple fluid flow channels. Intermediate portion 110 preferablycontains at least two tray systems 114; and more preferably contains atleast three tray systems. Settler 110 also has an inside wall 120 whichdefines a settling zone, having an upper portion 122, intermediateportion 108, and a lower portion 124. The lower portion 124 of settler110 is operably related by connection in fluid flow communication, viaan alkylation catalyst conduit 126, with alkylation reactor 100 forreturning at least a portion of the catalyst phase contained in lowerportion 124 to alkylation reactor 100 for use as at least a portion ofthe catalyst. Conduit 126 is optionally operably related by connectionin fluid flow communication to a conduit 128 for removal of a portion ofthe catalyst phase for regeneration downstream. Upper portion 122 ofsettler 110 is operably related by connection in fluid flowcommunication to an alkylate containing product conduit 130 for removinga portion of the hydrocarbon phase contained in upper portion 122 ofsettler 110 for further processing and/or fractionation downstream. AnHF feed conduit 132 is operably related by connection in fluid flowcommunication to intermediate portion 108 of settler 110 at a locationabove the upper-most tray system 112 for introducing an HF containingfeed to intermediate portion 108.

According to the second embodiment of the present invention, thehydrocarbon feedstock, comprises, consists of, or consists essentiallyof an olefin and an isoparaffin. The olefin can be selected from thegroup consisting of propene, an olefin containing four carbon atoms permolecule (butenes), an olefin containing 5 carbon atoms per molecule(pentenes), and combinations of any two or more thereof. Preferably theolefin contains four carbon atoms per molecule. The isoparaffin can beselected from the group consisting of an isoparaffin containing fourcarbon atoms per molecule, an isoparaffin containing 5 carbon atoms permolecule, and combinations of any two or more thereof. Preferably, theisoparaffin is isobutane.

The catalyst useful in the process can comprise, consist of, or consistessentially of hydrogen fluoride. The catalyst can also comprise,consist of, or consist essentially of hydrogen fluoride and water.Additionally, the catalyst can also comprise, consist of, or consistessentially of hydrogen fluoride and a volatility reducing additive.Furthermore, the catalyst can also comprise, consist of, or consistessentially of hydrogen fluoride, a volatility reducing additive, andwater.

The volatility reducing additive can be any compound effective inreducing the volatility of a mixture resulting from the addition of thevolatility reducing additive to hydrofluoric acid. More particularly,the volatility reducing additive can be a compound selected from thegroup consisting of sulfone, ammonia, methylamines, ethylamines,propylamines, butylamines, pentylamines, pyridine, alkylpryidines,melamine, hexamethylene-tetramine and the like, and combinations of anytwo or more thereof.

The sulfones suitable for use in this invention are the sulfones of thegeneral formula

R—SO₂—R¹

wherein R and R¹ are monovalent hydrocarbon alkyl or aryl substituents,each containing from 1 to 8 carbon atoms, and wherein R and R¹ can bethe same or different. Examples of suitable sulfones include, but arenot limited to, dimethylsulfone, di-n-propylsulfone, diphenylsulfone,ethylmethylsulfone and alicyclic sulfones wherein the SO₂ group isbonded to a hydrocarbon ring. In such a case, R and R¹ are formingtogether a branched or unbranched hydrocarbon divalent moiety preferablycontaining from 3 to 12 carbon atoms. Among the latter,tetramethylenesulfone or sulfolane, 3-methylsulfolane and2,4-dimethylsulfolane are more particularly suitable since they offerthe advantage of being liquid at process operating conditions of concernherein. These sulfones may also have substituents, particularly one ormore halogen atoms, such as for example, chloromethylethylsulfone. Thesesulfones may advantageously be used in the form of mixtures of any twoor more thereof. The most preferred volatility reducing additive issulfolane.

The hydrocarbon feedstock is contacted with the catalyst in thealkylation reaction zone to thereby produce alkylation of at least aportion of the olefins and isoparaffins in the form of an alkylationreaction effluent. The alkylation reaction effluent is then passed fromthe alkylation reaction zone to the intermediate portion of the settler,as previously described in the first embodiment, at a location below thelower-most tray system. A phase separation then occurs producing acatalyst phase and a hydrocarbon phase comprising alkylate and organicfluorides. The alkylate generally comprises alkylated hydrocarbonshaving from 5 to 20 carbon atoms per molecule, unreacted branched chainparaffin hydrocarbons, and isopentane. The organic fluorides are presentin the hydrocarbon phase generally in the range of from about 150 ppmwto about 10,000 ppmw, based on the total weight of the hydrocarbonphase. More typically, the concentration of the organic fluorides is inthe range of from about 200 ppmw to about 1,000 ppmw; and most typicallyfrom 250 ppmw to 500 ppmw, based on the total weight of the hydrocarbonphase.

An HF containing stream comprising greater than about 80 wt. % and lessthan about 94 wt. % hydrogen fluoride, preferably greater than about 85wt. % and less than about 94 wt. %, and most preferably greater thanabout 85 wt. % and less than about 90 wt. % hydrogen fluoride, is passedto the intermediate portion of the settler at a location above theupper-most tray system. At least a portion of the hydrocarbon phasecoalesces under each of the perforated trays of the tray systems therebyproviding a hydrocarbon layer under each of the perforated traysenabling a steady state volume of hydrogen fluoride to collect on thetop surface of each of the perforated trays. The height of such steadystate volumes of hydrogen fluoride can range from about 2 inches toabout 22 inches, preferably from about 4 to about 8 inches above the topsurfaces of each of the perforated trays.

For each of the tray systems, at least a portion of the hydrocarbonlayer accumulated below the perforated tray is allowed to pass upthrough the perforated tray in the form of droplets for contact with thesteady state volume of hydrogen fluoride on top of the perforated tray.The plurality of perforations in each of the perforated trays aredefined such that the droplets formed from the hydrocarbon layer have aSauter mean diameter greater than or equal to about 250 micrometers andless than or equal to about 5000 micrometers, preferably greater than orequal to about 1500 micrometers and less than or equal to about 2500micrometers.

A treated hydrocarbon phase passes up out of the intermediate portion ofthe settler into the upper portion of the settler. The cumulativecontact time of the hydrocarbon phase with the hydrogen fluoridecontained in the steady state volumes of hydrogen fluoride in theintermediate portion of the settler is greater than or equal to about0.5 seconds, preferably greater than or equal to about 0.5 seconds andless than or equal to about 2.5 seconds, and more preferably greaterthan or equal to about 0.5 seconds and less than or equal to about 2.0seconds. The treated hydrocarbon phase contains less organic fluoridethan the hydrocarbon phase. The treated hydrocarbon phase is removedfrom the upper portion of the settler for downstream processing andblending. The catalyst phase is removed from the lower portion of thesettler and a portion of the catalyst phase is used as at least aportion of the catalyst in the alkylation reaction zone, with thebalance sent downstream for catalyst regeneration.

The following example is provided to further illustrate this inventionand is not to be considered as unduly limiting the scope of thisinvention.

EXAMPLE

The feeds used in these runs were authentic refinery samples of either atotal settler effluent sample or an alkylate sample. The reactor(s) usedwere one inch diameter Monel® schedule 40 pipe of either eight orsixteen inch lengths. The diameters of the feed nozzles used were either0.010; 0.028 or 0.061 inch with a 0° spray angle. The acid phase was a99% hydrogen fluoride/1% water blend, circulated with a magneticallydriven gear pump. Initial Run A was designed as a base case with atarget residence time of 1.5 seconds and nominal 2000 μm Sauter meandiameter (SMD) droplets. All Runs were conducted at 100±2° F. For eachRun, the hydrocarbon feed was passed up through the nozzle, creatingdroplets, which then passed through the eight or sixteen inch layer ofacid phase whereupon samples of the treated hydrocarbons were collectedand analyzed by gas chromatography (GC).

The results for each Run are presented in the Table I below.

TABLE I Run A B C D Reactor Length, inches 8 8 16 8 Nozzle Diameter,inches 0.028 0.010 0.028 0.061 231 277 255 255 Estimated Droplet SMD, μm~2000 <500 2000 >3000 Feed Feed Component (A & B) 5 hrs 22 hrs 46 hrs.26 hrs. (C & D) 5 hrs. 23 hrs. 7 hrs. 13.75 hrs Lights¹ 0.04 0.05 0.020.02 0.01 0.11 0.02 0.03 0.21 0.03 Propane 8.37 8.16 8.16 8.06 7.81 8.088.43 8.03 7.76 6.95 Isobutane 55.13 53.31 52.95 52.76 53.61 54.64 52.8753.70 53.23 52.88 n-butane 8.22 8.20 8.08 8.16 8.26 8.08 8.13 8.30 8.208.32 Olefin 0.08 0 0 0 0 0.08 0 0 0 0 HC4F 0.11 0 0 0 0 0.11 0 0 0 0HC3F 0.25 0 0 0 0 0.24 0 0 0 0 i-pentane 3.62 4.31 4.32 4.34 4.39 3.585.41 5.30 4.44 4.59 n-pentane 0.04 0.04 0.04 0.04 0.04 0.04 0.05 0.050.04 0.05 2,2-dimethylbutane 0 0 0 0 0 0 0.02 0 0 0 2,3-dimethylbutane1.38 1.57 1.56 1.61 1.66 1.39 1.51 1.60 1.57 1.64 2-methylpentane 0.240.40 0.42 0.41 0.42 0.25 0.56 0.56 0.41 0.42 3-methylpentane 0.11 0.180.19 0.19 0.19 0.11 0.25 0.25 0.18 0.19 2,4-dimethylpentane 2.49 3.143.18 3.20 3.76 2.54 2.75 2.99 2.92 3.08 2,2,3-trimethylbutane 0.02 0.030.04 0.03 0.04 0.03 0.04 0.04 0.04 0 2-methylhexane 0.10 0.20 0.21 0.200.23 0.10 0.25 0.26 0.19 0.19 2,3-dimethylpentane 6.56 6.06 6.02 6.185.19 6.69 5.53 5.30 6.24 6.60 3-methylhexane 0.08 0.14 0.16 0.15 0.160.08 0.18 0.19 0.14 0.14 2,2,4-trimethylpentane 4.60 4.75 4.84 4.93 4.864.75 4.36 4.35 4.82 5.09 2,5-dimethylhexane 0.54 0.68 0.72 0.71 0.760.57 0.73 0.75 0.69 0.72 2,4-dimethylhexane 0.66 0.77 0.81 0.80 0.830.69 0.80 0.81 0.79 0.82 2,2,3-trimethylpentane 0.08 0.13 0.14 0.14 0.140.09 0.16 0.17 0.14 0.14 2,3,4-trimethylpentane 1.88 1.77 1.79 1.82 1.501.96 1.68 1.56 1.85 1.95 2,3,3-trimethylpentane 0.82 0.91 0.95 0.95 0.990.86 0.85 0.86 0.93 0.96 2,3-dimethylhexane 0.63 0.63 0.65 0.65 0.550.66 0.63 0.60 0.66 0.69 2-methylheptane 0 0 0 0 0. 0 0.05 0.05 0 03,4-dimethylhexane 0.08 0.09 0.09 0.09 0.10 0.08 0.09 0.09 0.09 0.093-methylheptane 0 0 0 0 0 0 0.04 0 0 0 2,2,5-trimethylhexane 0.72 0.920.98 0.96 1.03 0.77 1.00 1.03 0.95 0.99 Residue 3.15 3.56 3.68 3.60 3.473.42 3.61 3.13 3.51 3.47 [Total] 100 100 100 100 100 100 100 100 100 100HC4F ppmw F by gc 354 0 0 0 0 354 0 0 0 0 HC3F ppmw F by gc 1125 0 0 0 01090 0 0 0 0 ¹unidentified C1-C4 components

The results from the GC analysis showed a complete absence of detectablelevels of 2-fluoropropane (HC3F) and 2-fluoro-2-methylpropane (HC4F).The detection limit for alkyl fluorides for the GC is believed to bearound 15 ppmw. It was determined that the peak corresponding to HC4Fwas potentially masked by the n-butane signal. Similarly, the HC3F peak,at these low concentrations of HC3F relative to isobutane, was probablyjust not observable.

Thus, it was decided to boil off the isobutane from the samples andanalyze the stabilized alkylate product for alkylate range organicfluorides (primarily HC₅F) using an electrolytic conductivity detection(ELCD) instrument. This instrument responds only to total fluoride withno speciation. The boiled off samples (both feed and product) werere-analyzed using GC to determine HC3F and HC4F levels (if any), and theconcentration of C₅+ organic fluorides was determined based on the newGC data and the ELCD total fluoride values. The research octane number(RON) and motor octane number (MON) were calculated from the GC databased on the C₅+ components only for the feed and products for each Run.The results of the GC and ELCD analyses and the RON and MON estimationsare presented in Table II below.

TABLE II Run A B C D Reactor Length, inches 8 8 16 8 Nozzle Diameter,inches 0.028 0.01 0.028 0.061 Feed Rate, mL/hr 231 277 255 255 EstimatedDroplet SMD, μm ~2000 <500 2000 >3000 ELCD Results: Weathered SamplesComponent Feed 5 hrs 22 hrs 46 hrs 26 hrs 5 hrs 23 hrs 7 hrs 13.75 hrsTotal F, ppmw (by ELCD) 177 69.9 73.3 52 51.6 35.9 42.8 80.6 63.2 C3F,ppmw (by GC) 15 0 0 0 0 0 0 0 0 C4F, ppmw (by GC) 22 0 0 0 0 0 0 0 0C5F, ppmw ¹ 140 69.9 73.3 52 51.6 35.9 42.8 80.6 63.2 % Total AlkylFluoride 60.5% 58.6% 70.6% 70.8% 79.7% 75.8% 54.5% 64.3 Conversion Run AB C D Feed Average 26 hrs. Average Average RONgc 90.80 90.06 89.55 89.4190.01 MONgc 89.06 88.43 88.04 87.78 88.39 Delta RON −0.74 −1.25 −1.02−0.42 Delta MON −0.63 −1.02 −1.06 −0.45 ¹ calculated by subtracting HC3Fand HC4F concentrations from the ELCD total result.

As can be seen from Table II, the conversion of HC5F fluorides washigher in Run B wherein the droplet SMD was <500 as compared to the HC5Fconversion in Run A wherein the droplet SMD was ^(˜)2000. However, thedelta RON and delta MON for Run B were significantly higher than for RunA. Thus, while smaller droplets appear to result in greater HC5Fconversion, there is a corresponding octane reduction for the alkylatewhich would likely be unacceptable to most refiners.

Also, the conversion of HC5F fluorides was higher in Run C wherein thereactor length was sixteen inches as compared to the HC5F conversion inRun A wherein the reactor length was eight inches. However, the deltaRON and delta MON for Run C were significantly higher than for Run A.Thus, while longer contact times appear to result in greater HC5Fconversion, there is a corresponding octane reduction for the alkylatewhich would likely be unacceptable to most refiners.

In addition, the conversion of HC5F fluorides was on average lower inRun D wherein the droplet SMD was >3000 as compared to the HC5Fconversion in Run A wherein the droplet SMD was ^(˜)2000. The delta RONand delta MON for Run D were lower than for Run A. Thus, while largerdroplets appear to result in less alkylate octane degradation, thecorresponding reduction in HC5F conversion would make the use of suchlarger droplets impractical.

While this invention has been described in detail for the purpose ofillustration, it should not be construed as limited thereby but intendedto cover all changes and modifications within the spirit and scopethereof.

1. A system comprising: a) an alkylation reactor; b) a settler, havingan upper portion, an intermediate portion, and a lower portion whereinsaid intermediate portion contains at least one tray system comprising aperforated tray defining a plurality of perforations and a layer ofpacking below said perforated tray; c) a feed conduit operably relatedin fluid flow communication to said alkylation reactor; d) a settlerfeed conduit operably related in fluid flow communication to saidalkylation reactor and to said intermediate portion of said settler at alocation below said lower-most tray system; e) an HF feed conduitoperably related in fluid flow communication to said intermediateportion of said settler at a location above said upper-most tray system;f) an alkylate containing product conduit operably related in fluid flowcommunication to said upper portion of said settler; and g) analkylation catalyst conduit operably related in fluid flow communicationto said lower portion of said settler and to said alkylation reactor. 2.The system as recited in claim 1 wherein said intermediate portioncontains at least two of said tray systems.
 3. The system as recited inclaim 1 wherein said intermediate portion contains at least three ofsaid tray systems.
 4. The system as recited in claim 1 wherein saidpacking is selected from the group consisting of pall rings, raschigrings, berl saddles, intalox saddles, tellerettes, and combinations ofany two or more thereof.
 5. The system as recited in claim 1 whereinsaid packing comprises structured packing defining multiple fluid flowchannels.